This invention relates to an air conditioning unit or more in particular to a control apparatus including a circuit for protecting the compressor motor used with the refrigeration system of the air conditioning unit.
In conventional air conditioning units, the control apparatus includes a protecting device for protecting the compressor motor. Generally, before equalization of refrigerant pressure in the refrigeration system after stoppage of the compressor motor for some reason or other, the compressor motor with a low starting torque cannot restart over the refrigerant pressure. Unless the compressor motor restarts, an excess current flows in the compressor motor thereby to damage the same. Assume, for instance, that the indoor temperature reaches an appropriate level and the compressor motor stops. Immediately after that, when the air temperature becomes improper, the compressor motor cannot restart even if the current is made to flow in the compressor motor.
An ordinary protecting device cuts off the current in the compressor motor until the lapse of a predetermined length of time after the stoppage of the compressor motor, thus protecting the compressor motor. The length of time for which the current is required to be cut off is equal to the time required for equalization of the refrigerant pressure.
A conventional protecting device made up of mechanical parts is disclosed in detail in the U.S. Pat. No. 3,054,271 entitled "Automatic Controls for Air Conditioning Unit".
An electrical protecting device includes an electronic timer for determining the time required for cutting off the current flowing in the compressor motor. When the power supply is cut off, this electronic timer generally loses its functions as a timer, while at the same time disabling the functions of the protecting device. When the source current is thrown off temporarily and resupplied, therefore, the compressor motor is locked so that an excess current flows in the compressor motor.
Another type of protecting device has a function to cut off the current in the compressor motor when the power switch is closed after the stoppage of the compressor motor. This type of protecting device is such that the compressor motor is protected even in the case where the source current is cut off temporarily and resupplied. In the air conditioning unit having this type of protecting device, however, the compressor motor is not actuated until the lapse of a predetermined length of time after supply of the source current even if the refrigerant pressure is equalized, thus deteriorating the high response required of the air conditioning unit.